Cancer is one of the greatest concerns worldwide, because of the high mortality rates, the economic and social burden associated with it and the psychological issues faced by cancer survivors.
Resistance to treatments is generally acquired when tumor mass presents areas which are not reached or affected by conventional therapies, i.e. chemotherapy or radiotherapy. These regions are located at the centre of the tumor bulk and are generally characterised by a highly hypoxic environment, meaning that the oxygen supply is insufficient for the appropriate respiration of cells and stroma (Shannon, A. M., D. J. Bouchier-Hayes, C. M. Condron and D. Toomey, 2003 Tumour hypoxia, chemotherapeutic resistance and hypoxia-related therapies. Cancer Treatment Reviews 29: 297-307). The hypoxic condition, which is an invariable characteristic of solid tumors, develops because the rate of cell replication in tumors overcomes that of vessel formation: continuous demand of oxygen, thus, is detected by cellular oxygen sensors which address the need by stimulating the angiogenic sprouting. In turn, angiogenesis leads to the generation of structurally disordered blood vessels with improper distribution within the cancer mass (Kandel, J. J., D. J. Yamashiro and J. Kitajewski, 2011 Angiogenesis in Tumour Development and Metastasis, pp. 81-93 in Therapeutic Angiogenesis for Vascular Diseases: Molecular Mechanisms and Targeted Clinical Approaches for the Treatment of Angiogenic Disease, edited by M. Slevin. Springer-Verlag Berlin, Berlin): this causes the development of a dysfunctional microvasculature that leads to the inadequate diffusion and perfusion of oxygen throughout the mass of tumor (Vaupel, P., O. Thews and M. Hoeckel, 2001 Treatment resistance of solid tumors—Role of hypoxia and anemia. Medical Oncology 18: 243-259). Ultimately, this creates a feedback loop which further increases hypoxia.
An important feature of hypoxic areas of cancers is the marked presence of immune cells, which infiltrate into the tumor mass since the very early stages of cancer onset (Di Caro, G., F. Marchesi, L. Laghi and F. Grizzi, 2013 Immune cells: plastic players along colorectal cancer progression. Journal of Cellular and Molecular Medicine 17: 1088-1095). Among the most studied cell types are tumor-associated macrophages (TAMs). TAMs are a population of macrophages that mobilise and accumulate in great number in the hypoxic central areas of solid tumors (Turner, L., C. Scotton, R. Negus and F. Balkwill, 1999 Hypoxia inhibits macrophage migration. European Journal of Immunology 29: 2280-2287; Lewis, J. S., R. J. Landers, J. C. E. Underwood, A. L. Harris and C. E. Lewis, 2000 Expression of vascular endothelial growth factor by macrophages is up-regulated in poorly vascularized areas of breast carcinomas. Journal of Pathology 192: 150-158; Gollapudi, K., C. Galet, T. Grogan, H. Zhang, J. W. Said et al., 2013 Association between tumor-associated macrophage infiltration, high grade prostate cancer, and biochemical recurrence after radical prostatectomy. American Journal of Cancer Research 3: 523-529). TAMs are characterised by a specific phenotype, activated in response to micro-environmental signals such as cytokines, growth factors and hormones (Martinez, F. O., S. Gordon, M. Locati and A. Mantovani, 2006 Transcriptional profiling of the human monocyte-to-macrophage differentiation and polarization: New molecules and patterns of gene expression. Journal of Immunology 177: 7303-7311), that are often referred to as M2 macrophages. While their counterparts, M1-polarised macrophages, are activated in response to inflammatory molecules and are characterised by high anti-tumor and immuno-stimulatory functions, the M2-skewed macrophages express marked pro-tumor activities, suppressing inflammatory processes and promoting matrix remodelling, invasion, angiogenesis and survival (Sica, A., T. Schioppa, A. Mantovani and P. Allavena, 2006 Tumour-associated macrophages are a distinct M2 polarised population promoting tumour progression: Potential targets of anti-cancer therapy. European Journal of Cancer 42: 717-727).
TAMs are known to be recruited from the blood circulation by chemotactic cytokines which are continuously released by tumor cells; for instance, MCP-1, VEGF and CSF-1 expression was found to be positively correlated with TAM accumulation in numerous human tumors (Graves, D. T., R. Barnhill, T. Galanopoulos and H. N. Antoniades, 1992 EXPRESSION OF MONOCYTE CHEMOTACTIC PROTEIN-1 IN HUMAN-MELANOMA INVIVO. American Journal of Pathology 140: 9-14; Kacinski, B. M., 1995 CSF-1 AND ITS RECEPTOR IN OVARIAN, ENDOMETRIAL AND BREAST-CANCER. Annals of Medicine 27: 79-85. Arenberg, D. A., M. P. Keane, B. DiGiovine, S. L. Kunkel, S. R. B. Strom et al., 2000 Macrophage infiltration in human non-small-cell lung cancer: the role of CC chemokines. Cancer Immunology Immunotherapy 49: 63-70; Lewis, J. S., R. J. Landers, J. C. E. Underwood, A. L. Harris and C. E. Lewis, 2000 Expression of vascular endothelial growth factor by macrophages is up-regulated in poorly vascularized areas of breast carcinomas. Journal of Pathology 192: 150-158). However, their specific accumulation into hypoxic regions of tumors is fostered by several features: the marked presence of necrotic cells (Lewis, J., R. J. Landers, R. D. Leek, K. Corke, A. L. Harris et al., 1997 Role of macrophages in tumour angiogenesis: Regulation by hypoxia. Journal of Pathology 182: A1-A1) and the release of a number of chemo-attractants, such as MCP-1 (Li, X., H. Kimura, K. Hirota, H. Sugimoto and H. Yoshida, 2005 Hypoxia reduces constitutive and TNF-alpha-induced expression of monocyte chemoattractant protein-1 in human proximal renal tubular cells. Biochemical and Biophysical Research Communications 335: 1026-1034), VEGF (Brown, L. F., B. Berse, R. W. Jackman, K. Tognazzi, A. J. Guidi et al., 1995 EXPRESSION OF VASCULAR-PERMEABILITY FACTOR (VASCULAR ENDOTHELIAL GROWTH-FACTOR) AND ITS RECEPTORS IN BREAST-CANCER. Human Pathology 26: 86-91) and endothelins (Grimshaw, M. J., S. Naylor and F. R. Balkwill, 2002 Endothelin-2 is a hypoxia-induced autocrine survival factor for breast tumor cells. Molecular Cancer Therapeutics 1: 1273-1281). Once amassed into hypoxic areas, TAMs respond to oxygen-depleted conditions through an increase in production and release of several factors, such as growth factors, MMPs and CXCLs, which in turn affect angiogenesis, cellular growth, invasive capabilities and metastasis: thus, TAMs ultimately promote tumor progression (Sica, A., T. Schioppa, A. Mantovani and P. Allavena, 2006 Tumour-associated macrophages are a distinct M2 polarised population promoting tumour progression: Potential targets of anti-cancer therapy. European Journal of Cancer 42: 717-727).
Given their pivotal role in triggering cancer progression, infiltration of TAMs in tumors has been correlated with poor prognosis in the majority of solid cancers: lung cancer (Chen, J. J. W., Y. C. Lin, P. L. Yao, A. Yuan, H. Y. Chen et al., 2005 Tumor-associated macrophages: The double-edged sword in cancer progression. Journal of Clinical Oncology 23: 953-964), oral squamous cell carcinoma (He, K.-F., L. Zhang, C.-F. Huang, S.-R. Ma, Y.-F. Wang et al., 2014 CD163+ Tumor-Associated Macrophages Correlated with Poor Prognosis and Cancer Stem Cells in Oral Squamous Cell Carcinoma. BioMed research international 2014: 838632), papillary thyroid carcinoma (KIM et al. 2013), papillary renal cell carcinoma (Behnes, C. L., F. Bremmer, B. Hemmerlein, A. Strauss, P. Strobel et al., 2014 Tumor-associated macrophages are involved in tumor progression in papillary renal cell carcinoma. Virchows Archiv 464: 191-196), breast cancer (Mukhtar, R. A., A. P. Moore, V. J. Tandon, O. Nseyo, P. Twomey et al., 2012 Elevated Levels of Proliferating and Recently Migrated Tumor-associated Macrophages Confer Increased Aggressiveness and Worse Outcomes in Breast Cancer. Annals of Surgical Oncology 19: 3979-3986; Tang, X. Q., 2013 Tumor-associated macrophages as potential diagnostic and prognostic biomarkers in breast cancer. Cancer Letters 332: 3-10), ovarian cancer (Lan, C. Y., X. Huang, S. X. Lin, H. Q. Huang, Q. C. Cai et al., 2013 Expression of M2-Polarized Macrophages is Associated with Poor Prognosis for Advanced Epithelial Ovarian Cancer. Technology in Cancer Research & Treatment 12: 259-267) and pancreatic cancer (Kurahara, H., S. Takao, T. Kuwahata, T. Nagai, Q. Ding et al., 2012 Clinical Significance of Folate Receptor beta-expressing Tumor-associated Macrophages in Pancreatic Cancer. Annals of Surgical Oncology 19: 2264-2271).
Oncolytic virotherapy concerns the use of lytic viruses which selectively infect and kill cancer cells. Some oncolytic viruses are promising therapies as they display exquisite selection for replication in cancer cells and their self-limiting propagation within tumors results in fewer toxic side effects. Several oncolytic viruses have shown great promise in the clinic (Bell, J., Oncolytic Viruses: An Approved Product on the Horizon? Mol Ther. 2010; 18(2): 233-234).
Macrophages are known to have a natural homing ability to a site of disease and have been proposed as cellular vehicles for gene therapy (Burke et al., Macrophages in gene therapy: cellular delivery vehicles and in vivo targets. Journal of Leukocyte Biology Vol. 72, no. 3 417-428).
WO2007/113572 describes monocyte derived cells, e.g. macrophages, that comprise a magnetic material. The cells are described to be useful as a vehicle for targeting a therapeutic agent to a diseased material in a subject, where the therapeutic agent may preferably be a gene (i.e. a gene therapy approach to treatment of the diseased material) and the subject requiring treatment is exposed to a magnetic field to assist location of the cells in the diseased material. Related work is disclosed in Muthana et al. A novel magnetic approach to enhance the efficacy of cell-based gene therapies. Gene Therapy (2008) 15, 902-910.
Muthana et al., (Use of Macrophages to Target Therapeutic Adenovirus to Human Prostate Tumors. Cancer Res; 71(5) Mar. 1, 2011) describe an approach to treatment of prostate tumors in which macrophages were transduced with a hypoxia-regulated E1A/B construct and an E1A-dependent oncolytic adenovirus, whose proliferation was also restricted to prostate tumor cells using prostate-specific promoter elements to control E1A expression. In these experiments the macrophages were used as ‘silent carriers’ of the adenovirus which was only induced to replicate upon location in a hypoxic environment. Induction of replication of adenovirus did not lead to death of the macrophages. In Muthana et al., (Macrophage Delivery of an Oncoloytic Virus Abolishes Tumor Regrowth and Metastasis after Chemotherapy or Irradiation. Cancer Res; 73(2) Jan. 15, 2013) the authors describe experiments using the same adenoviral approach to investigate the effects post-administration of docetaxel or radiation therapy.